1. Field of the Invention
The present invention relates to a method of recording and playback of video information and the like using a disk-shaped optical information recording medium which is recordable, reproducible, and erasable (called optical disk hereafter) and more particularly, to a method for high-speed recording and playback of a large amount of video information and the like by simultaneously using both sides of an optical disk.
2. Description of the Related Art
In recent years, optical disks that record and play back video information only one side of the disk have reached the market, and they have been used for editing and presentation, taking advantage of their characteristics such as good retrieval performance and lasting image quality not degraded by long-time playback. Optical disks presently available have difficulties in recording video information in digital form, because the amount of information is great and a high transfer rate is required. For example, a video signal of the NTSC system and the like is frequency-modulated and recorded in analog form. However, recent development in image compression techniques in digital signal processing has enabled one to obtain a digital image of high quality with a smaller amount of information than before, so that recording digital image information in real time has become possible using a comparatively small number of scanners (optical heads) such as two scanners. The digital recording can record images of high quality which are substantially free of image turbulence (called drop out hereafter), which is a problem of analog recording, due to flaws or foreign material on the disk, and the continuous recording time can be made longer by simultaneously using both sides of the optical disk. An optical disk recorder that records and plays back video information has to start recording and playback at a definite base position of a circle on the disk concentric with its circumference in order to obtain stable images at a discontinuous point where an additional recording starts. As proposed in Japanese laid-open Patent publication Sho 61-32265, prior apparatus adopted a method of controlling the starting and ending of recording based on a recording alignment mark made by pre-formatting the optical disk in the manufacturing process or by recording in the address signal part of each sector of the disk.
However, a double-sided optical disk used in simultaneous recording and playback is made by joining two pre-formatted single-sided optical disks together, so that an adjustment of the dynamic balance of the disks in the manufacturing process of the disk is indispensable. Therefore, the positions of the recording alignment marks on the front and reverse sides of the disk differ by a maximum of 360 degrees, so that if a video signal is recorded on both sides of the disk following a prior method, then the starting points of recording differ by a maximum of one revolution. In a system of recording one picture per revolution, it delays for a time period taken by one revolution on each side for a recording of one picture, so that a maximum time period taken by two revolutions is required to start recording. This delay is the same for playback. Therefore, the time required for recording or playback is a maximum of one revolution period longer than in the single-sided disk, and a dispersion of one revolution period occurs depending on disks. In order to absorb this dispersion and make constant the recording and playback time, a buffer memory corresponding to more than one frame for adjusting the time for recording and playback becomes necessary, so that costs of the apparatus becomes inconveniently higher.